General Motors has wowed electrified vehicle enthusiasts by announcing the most effective plug-in hybrid – the 2016 Volt – and one of the highest-mpg midsized sedans – the 2016 Malibu Hybrid – but a mystery surrounds these cars’ comparative efficiency.
The issue is this: The 1.5-liter-based Volt’s drive unit – its electrified transmission – and other “propulsion system” hardware were incorporated into the 1.8-liter Malibu Hybrid but somehow the larger more powerful Malibu is up to 15-percent more fuel efficient in gas-only operation.
GM is estimating the extended-range electric Volt will see a combined EPA rating of 41 mpg when running in “charge sustaining” (hybrid) mode on gas, and the new Malibu ought to be good for 47.
Update:After this was written the Malibu Hybrid’s EPA number came in at 46 mpg, but the rest of this article remains accurate.
So what gives? Did GM learn a trick or two with the Malibu to let it beat the Volt using its own technology? Did an independent Malibu development team choose a slightly different path and wind up out-doing the premier Volt product in a certain respect?
The fact that on paper one might expect mpg roles ought to be reversed with the Volt equaling or beating the Malibu Hybrid has not been lost on readers at GM-Volt.com, many of which are engineers and deeply knowledgeable of these technologies.
“I am puzzled why the Volt can’t at least match the Malibu Hybrid’s highway mpg given it has a similar powertrain and surely has a lower CDa,” said one GM-Volt poster.
“Maybe Jesse Ortega can tell Andrew Farah how he got 47 mpg out of the Voltec power train in hybrid mode,” said another GM-Volt reader speaking of the respective lead engineers behind the Malibu and Volt.
Whether the answer will matter to fuel consumed or CO2 emitted is an open question given that GM OnStar data has shown as much as 80 percent of daily Volt driving is on battery power and forgoes the gas engine.
Further, GM says it expects the 2016 Volt will see 90 percent EV operation day to day, so gas engine efficiency is secondary to 50 miles EV range and stellar miles per gallon equivalent (MPGe) the Volt offers which the Malibu does not.
Chevrolet communications reps said this while not granting repeated requests for a follow-up interview with lead Malibu Hybrid engineer Daryl Wilson to shed greater light on the subject.
“Volt and Malibu Hybrid serve a different purpose for a different customer set,” said Chevrolet communications rep Chad Lyons. “One tries to maximize the use of gasoline (Malibu), while the other tries to not use gasoline at all, unless they have to (Volt). A more accurate comparison, would be to look at the MPGe rating of the Volt vs MPG rating of the Hybrid.”
Be that as it may, “MPGe” only works while the Volt’s battery is charged. Otherwise, it morphs back to a hybrid that works much like the Malibu Hybrid does full time.
What’s more, Chevrolet alternately touts the Volt as a “range-extended electric vehicle” meaning going past EV miles prevents “range anxiety.” So, if you want to travel farther than 50 miles, the Volt allows that – and under those conditions is mpg irrelevant?
Energy efficiency for any vehicle is a function of several key factors. Let’s briefly sum these for the Volt and Malibu Hybrid.
The Volt uses a 1.5-liter gas engine adopted from GM’s family of new small engines.
The direct-injected, naturally aspirated powerplant developed for global vehicles is tuned for use in the 2016 Volt and is 100cc larger than the 1.4-liter GM used in the 2011-2015 Volt.
By contrast, the Malibu Hybrid uses an “all-new” 1.8-liter from a different engine family and less is known about it. It is believed to be cutting edge and does employ GM’s first use of Exhaust Gas Heat Recovery (EGHR) which limits the gas engine having to be run on cold days as often or at all.
EGHR – not to be confused with EGR (Exhaust Gas Recirculation) which both vehicles employ – helps bring a cold gas engine up to a temperature more quickly so it can run at peak efficiency and also helps provide warm cabin air when needed via a heat exchanger. The Volt does not have this feature.
In our interview this month in New York with Wilson, he said EGHR can improve efficiency by “more than 10 mpg” in a “cold CO” test, one of the EPA’s five test cycles. This is a low-speed up and down cycle where the vehicle is run in chilly air that’s just 20 degrees Fahrenheit.
“That’s the kind of efficiency difference that you’ll see with this technology.” said Wilson of the technology that helps prevent the engine from running just to provide heat.
How this would play into the Malibu Hybrid’s overall EPA results is unclear but it may help particularly on cold days.
Powertrain Output and Efficiency
Both hybrid vehicles pair their respective four-cylinder gas engines to similar drive units – i.e., the electrified transaxle and the vehicles merge battery power into their net output.
The Volt’s smaller direct-injected DOHC 1.5-liter engine is rated 101 horsepower at 5,600 rpm and combined with electrics, system output is 149 horsepower.
The Malibu’s direct-injected 1.8 is more powerful but unlisted is its specific output. System power combined is 182.
A deep dive into that transaxle was co-published by three engineers on the GM-Volt forum, including Jeff Nisewanger, a software developer in Silicon Valley, who was has long followed hybridization and was consulted on this article.
He has been actively following the Volt since the concept car was shown in 2007. In early January this year he googled GM’s many hybrid patents and correctly identified the one describing the transmission used in the new Volt and Malibu Hybrid.
The Volt’s larger battery also may give a slight advantage in that even when depleted, observes Nisewanger, the Volt can probably deliver 80-120 kilowatts for short periods (10 or more seconds) during acceleration or climbing modest hills.
“The Malibu battery, even though it is designed with power-optimized cells, is probably limited to no more than 68 kilowatts for short power bursts and is quite likely limited to 20-40 kilowatts most of the time,” said Nisewanger. “So, the Volt engine could start up less frequently due to torque demand (kilowatt output from the battery).”
As for curb weight, both cars may be within 150 pounds of each other. The new Volt is supposed to weigh over a couple hundred pounds less than the first generation, or around 3,550 pounds. The new non-hybrid Malibu is lighter than the 2015 Malibu at 3,100, and the heavier Malibu Hybrid weighs 3,400 pounds
Both cars are slippery in the wind tunnel. Coefficient of drag for the Malibu Hybrid is .294. The Volt is slightly better with a cd of .285. There is likely some variance but probably not a major one.
Tire Rolling Resistance
Both cars may run on similar sized low rolling resistance tires with the Malibu Hybrid’s being a bit wider. Specifically, Volt gets 215/50-17, and Malibu gets 225/55-17
While there are differences between the Volt and Malibu it is not empirically obvious why the bigger, more-powerful Malibu is up to 15-percent more efficient than the Volt when both are running on gasoline.
Notable is GM has not published city and highway mpg for the Volt like it has the Malibu Hybrid which is estimated at 48 and 45 respectably. Neither car has had EPA certified results announced, but GM says policy is to try to match its estimates with what will truly be on the window sticker.
Regarding curb weight, if the Malibu Hybrid’s edge were merely a weight question, the Volt might need to weigh significantly more to lose all the efficiency that it does. But it doesn’t so this line of inquiry is all but moot.
Aerodynamics may play a role as well, but the frontal profile of the Malibu is larger, so if anything it likely pushes more air suggesting it must overcome greater resistance than the Volt. Tire size too is similar, which brings us to the drivetrain.
GM upgraded the Volt’s engine over generation one partly so it could run on regular gas instead of the old engine’s premium, and partly because the new 1.5 liter is more efficient than the 37 mpg combined afforded for 2011-2015 models’ 1.4.
The larger engine need not work as hard generating power and this path was followed by Toyota in 2009 with the Prius which jumped from 1.5 liters to 1.8. The 2015 Prius has a curb weight of just 3,072 pounds, by the way, almost 500 pounds lighter than the Volt and Malibu estimates.
It can seem counterintuitive but a larger engine not only may produce less noise, vibration, and harshness, it can lope along more efficiently in a sweet spot of power-to-mpg. This thinking was followed by GM, just not to the degree that Toyota did with the current Prius.
It shares many design details with the Volt’s 1.5, but may differ in other ways internally, and it does the Volt one better with EGHR – a type of technology Toyota also employs on the Prius.
It is possible also, Nisewanger notes, that the Malibu Hybrid’s 1.8 liter is simply superior to what is in the Volt but might have a slightly higher production cost, or some other decision went into its selection.
The Volt was built under mandate to shave costs. In an interview, Volt lead engineer Andrew Farah sidestepped a pointed question asking how much GM managed to save, but implied cost cutting was done where feasible.
Otherwise, the Volt was built based on existing owner feedback to out-do the existing Volt, which it does, and its gasoline use has been seen as a secondary priority.
“Maybe the Malibu 1.8 liter is doing some tricks that give it a somewhat higher overall thermal efficiency,” speculates Nisewanger. “The 1.5-liter engine used in the Volt seems to be have been tweaked slightly for use in the Volt but perhaps the 1.8 liter was designed specifically for a new set of GM hybrid vehicles whereas the 1.5-liter Volt engine shares most of its design with the other three- and four-cylinder members of its engine family?
Does It Matter?
If these cars are about saving fuel and cutting greenhouse gas, both promise to be effective considering their different missions in life.
Assuming the Volt is operated 80 percent of the time in EV mode, and 20 percent in gas, for 12,000 miles annual usage, it would run the gas engine for just 2,400 of those miles.
At 41 mpg, this is 58.5 gallons of gas.
By contrast a Malibu Hybrid at 47 mpg would burn 255 gallons. An annual difference of 196.5 gallons and resultant CO2 emissions means the Volt still does a much better job of weaning us off of gas in the long run – although this also doesn’t account for any upstream emissions from respective energy grids used to generate electricity for the Volt.
Another factor is the distinct possibility that a Volt could very well have been a 47 up to nearly 50 mpg car that also delivered 50 miles EV range. Fuel savings between 41 mpg and 47 for 2,400 miles per year would only amount to 7.5 gallons but positive perception in the public’s eye could be worth something for the Volt’s sales and market acceptance. And, not everyone fits the idealized scenario, and some will want the Volt to go farther on gas, and to them it will matter more.
Further, Chevrolet does not exist in a vacuum. Although the Volt is for now the hands-down leader in EV range among plug-in gas-electric cars, competitors are coming.
The aforementioned Prius has a plug-in hybrid version which while often dismissed for just 11 miles EPA-rated range, does get 50 mpg in hybrid mode and is due for upgrade next year.
Toyota has said the new Prius will get 15-percent more economy which could mean 58 combined, and if Toyota increases PHEV electric range, say to closer to 20 miles, the disparity could be similar to that of the 2015 Volt and 2015 Prius PHEV.
Whether that is relevant is also up for debate, but clearly GM has made the Malibu Hybrid more efficient using the Volt’s own system while delivering much more roomy space in a car pushing close to Impala size.
Evidence suggests the primary reason is in the respective gas engines used.
“Other reasons might have been a need in the Volt to balance aspects of the transmission between optimizing the EV versus the gas engine efficiency and performance,” said Nisewanger. “The Malibu doesn’t have to do that.”
For its part however, Chevrolet says because different customers will use these cars differently, this discussion won’t be so meaningful.
“I fully understand your question but you need to really look at how Volt owners drive the vehicle,” said Chevrolet media rep Michelle Malcho. “Ninety percent of our owners will not even use the range extender with the new generation. So, obviously when it comes to how customers really use the car they are getting 250 MPGe. Not sure it is really helpful to look at hybrid vs. Volt powertrain except to understand that the hybrid benefits from Volt technology.”
Maybe so, but some of the most diehard Volt fans have been asking.
Some have also expressed fears that there may be no third-generation Volt as GM has not proliferated “Voltec” but instead re-engineered generation two to keep it in the stable and use it as seed stock for more hybrids and plug-in hybrids to come.
The Malibu Hybrid could easily be made into a plug-in hybrid such as Ford does with its Fusion and Fusion Energi Hybrid.
But this too is a given: progress marches on. Today the Volt offers more than double the EV range of the 19-mile Ford Fusion Energi, and beats the old Volt on gas; it has a revised back seat, smart new styling, and more.
It’s the best compromise within context, but is it? Or does the Malibu Hybrid show what else GM could have done?